In order to increase the recording density of current hard disk drives (HDDs), medium noise may be reduced, in some cases, thereby allowing for the signal that is readable from the HDD to be more pronounced.
The suppression of medium noise to a low level while maintaining resistance to heat and external magnetic fields in a magnetic recording medium for a high-density magnetic storage apparatus, such as a HDD, has been pursued in the field for some time. The CoCrPt alloy recording layer used in conventional media uses the phase separation of Co and Cr to segregate non-magnetic elements, such as Cr, at grain boundaries. A large quantity of the non-magnetic elements forming the grain boundary may be added in order to reduce medium noise. However, many of these elements are not completely segregated at the grain boundaries and often remain in the crystal grains. Thus, the magnetic anisotropic energy decreases, and maintaining the signal quality is difficult. In contrast, because oxides and magnetic crystal grains are easily separated in a granular recording layer, the medium noise may be reduced while maintaining high magnetic anisotropic energy without needing to add a large quantity of nonmagnetic elements such as Cr. For example, medium performance may be improved by improving the recording layer, as described in Japanese Unexamined Patent Application Publication No. 2003-178413 and United States Patent Application Publication No. 2006/0121319.
Even in media using this kind of granular recording layer, the crystal grains and the recording magnetization unit (magnetic cluster size) of the recording layer may be finer, e.g., smaller in size, which will further reduce medium noise. The crystal grain diameter and the magnetic cluster size of the recording layer depend strongly on the seed layer and the intermediate layer used in constructing the magnetic media.
In particular, to obtain a steep recording magnetic field gradient as the distance decreases between the magnetic head and the soft-magnetic underlayer, it is useful to improve the crystal orientation of the recording layer in a thin intermediate layer and further miniaturize the crystal grains and the magnetic cluster size. For example, United States Patent Application Publication No. 2005/0202286, Japanese Patent No. 4,019,703, Japanese Unexamined Patent Application Publication No. 2002-334424, U.S. Pat. No. 7,641,989, United States Patent Application Publication No. 2009/0195924 and United States Patent Application Publication No. 2009/0116137 disclose methods for adding metal elements to an Ru intermediate layer and a granular intermediate layer with oxides added to the intermediate layer. However, although obtaining a constant effect was confirmed in these references, this effect was inadequate to realize a higher areal recording density.
Therefore, a magnetic recording medium that is capable of high recording density with low medium noise by reducing the magnetic cluster size without increasing the amount of oxide in the recording layer would be beneficial to the field of magnetic data reproduction.